Today, to achieve high-capacity optical communications, development of multichannel optical transceivers is in progress. For example, a transmission scheme using four 25-Gpbs channels in combination with pulse amplitude modulation is adopted in optical transceivers designed for 100 gigabit Ethernet.
A receiver optical subassembly (ROSA) is provided in the receiver frontend of an optical transceiver for optical-to-electrical conversion and amplification. To reduce the ROSA size, a compact design for incorporating a plurality of channels into a package is being adopted.
In multimode transmission using discrete photodetectors, independently adjustable optical delay devices are arranged on single-mode fiber optic cables connected to the associated photodetectors. The optical delay devices are controlled by a digital signal processor (DSP) to bring all the incoming light signals in synchronization with one another. See, for example, Patent Document 1 listed below.
Another known technique is an electronic circuit for use in parallel transmission of electrical signals, adapted to correct for or retime a skew or a difference in propagation delay time between the clock and synchronized parallel data. See, for example, Patent Document 2 listed below.